The present invention relates to generally a gear pump and more particularly a hydraulic circuit means adapted to lubricate and cool the shafts of a pair of intermeshing gears with low pressure liquid drawn through a suction port of the gear pump.
The lubricating means for lubricating the shafts of a pair of intermeshing gears with low pressure liquid drawn through a suction port of a gear pump are disclosed, for instance, in U.S. Pat. No. 3,447,472, granted to J. E. Hodges et al, June 3, 1969, and in U.S. Pat. No. 3,490,382 granted to P. G. Joyner, Jan. 20, 1970. According to these inventions, there is provided gearing including at least two meshing rotors of toothed or lobed form whose shafts are mounted in bushes there requiring lubrication, wherein grooving is formed in the bore of each bush which is in communication with a side face of its respective motor in a zone located at a position where, as the rotor teeth or lobes successively pass it, the spaces between the meshing teeth or lobes are increasing in volume, the consequent suction created by the increase in volume inducing liquid to flow through the grooving in the bushes, thus to lubricate the shafts as they run in the bushes.
However, during almost all the time when the space between the meshing teeth or lobes is increased, the space is communicated with the suction port through the backlash between the intermeshing teeth or lobes so that the liquid is drawn from the suction port into the space. As a result, at low rotational speed at which the suction created by the increase in volume is weak, the liquid flowing into the inter-teeth space is decreased considerably in volume so that the shafts of the gears cannot be sufficiently lubricated with the resultant excessive wear and abrasion of the shafts and bushes and seizures in the worst case.